The present invention relates generally to interconnection of conducting layers on a semiconductor device, and specifically to a method for selectively enlarging vias or contacts in dual damascene devices.
Semiconductor devices having two layers of metalization conventionally use metal-filled vias to electrically connect the layers at the appropriate points in the circuit. One conventional process, which is known as trench-first dual damascene via formation, involves forming the vias and the top metalization layer simultaneously.
In fabricating very large and ultra large scale integration circuits with the dual damascene process, an insulating or dielectric material, such as silicon oxide, of a semiconductor device is patterned with several thousand openings for the conductive lines and vias which are filled at the same time with metal, such as aluminum, and serve to interconnect the active and/or passive elements of the integrated circuit. The dual damascene process also is used for forming the multilevel conductive lines of metal, such as copper, in the insulating layers, such as polyimide, of multi-layer substrate on which semiconductor devices are mounted.
There are several problems involved in fabrication of vias in trench first dual damascene technology, however. In regard to metalization issues, the conductor fill process is facilitated by expanded via size. Statistical failures are made less probable by enlarging vias or contacts; thus, yields are increased. The lithography process for vias in a trench-first dual damascene integration scheme also is very difficult and the process latitude is very narrow. This limitation in process latitude is a result of two factorsxe2x80x94the severe topography of the trench-first damascene integration scheme creates via lithography problems, and the small (on the order of 0.25 micron) feature size necessary for the current technology. The vias need to be imaged in resist sitting in lines and pads of widely varying widths and pattern factors. For narrow lines, the local resist thickness at each via feature depends on the local pattern density of the trenches. For wide lines, because the resist relaxes into the already-etched pad or wide line, the resist surface drops down. The focus latitude, especially, can be too small to manufacture all types of via features consistently. Inconsistent via formation can lead to short circuits or undependable circuits.
What is needed in the art is method for forming vias that allows for greater quality and consistency.
The above-described and other disadvantages of the prior art are overcome or alleviated by the method of the present invention, which comprises selectively enlarging vias to expand the dimensions of those vias which are capable of expansion. The method for selective enlargement comprises: a) determining if a first side of a first via can be extended by comparison of expanded via edge position to applicable via-line and/or via-via minimum distance lay-out ground rules, b) extending said first side if it was determined said first side could be extended, and c) repeating steps a) and b) for the remaining sides of said first via.
The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.